The present invention relates to a unit for raising and lowering an agricultural implement connected to a tractor.
As is known, units of the above indicated type, include an hydraulic raising device and a device for attachment of the implement which serves to connect the implements controlled by the raising device to the tractor. This device includes two lower arms pivoted to a torsion bar supported by the body of the tractor, two vertical link rods which connect the lower arms to the raising device and a strut, the so-called top link, which is attachable to the implement at a central point. The raising device includes a rotatable bar having two lateral arms pivoted at the upper ends of the vertical link rods and an hydraulic distributor operable to actuate, via a control pump, one or more hydraulic cylinders which cause the bar to rotate to raise the implement by means of the lateral arms and the vertical link rods. The unit in question detects the forces on the lower arms of the attachment device of the implement by means of the torsion bar and allows the following modes of operation to be obtained: controlled position, floating position, controlled force, and joint control of force and position. Each of these possibilities is chosen, from time to time, in dependence on the required work, the type of implement and the consistency of the soil. The unit further includes a control and adjustment device by which selection of the above modes of operation is effected. This device has two levers by which the position of the implement with respect to the tractor is controlled. With the first lever, the implement's position is maintained fixed and controlled position working is obtained, while with the second lever the traction force required at the tractor is maintained constant in such a way that the implement automatically varies its position, thus obtaining controlled force working. The other modes of operation are obtained by suitably acting on the said levers.
By means of the said levers, therefore, the most suitable operating conditions for the type of ground to be worked can be chosen in dependence on the type of implement. Now it is apparent that when the tractor arrives at the outer edge of the field it is necessary first to raise the implement by acting on the levers, and subsequently, the tractor has to be turned around, and finally the implement must be lowered again and the two levers put back in the previous positions to allow the continuance of the work in the predetermined operating conditions. The main disadvantage of the units currently utilised lies precisely in the fact that, every time it is necessary to turn the tractor it is necessary to move the levers to raise the implement and then put these levers back into their previous positions. The operations indicated above are, in fact, complex and must be repeated whenever it is necessary to turn the tractor. Moreover, it is apparent that it is very difficult, after having turned the tractor round, to succeed in returning the two levers exactly to the previous positions,and therefore very difficult to obtain exactly the previous operating conditions of the implement.